Search

We report high-precision mass measurements of $^{50--55}\mathrm{Sc}$ isotopes performed at the LEBIT facility at NSCL and at the TITAN facility at TRIUMF. Our results provide a substantial reduction of their uncertainties and indicate significant deviations, up to 0.7 MeV, from the previously recommended mass values for $^{53--55}\mathrm{Sc}$. The results of this work provide an important update to the description of emerging closed-shell phenomena at neutron numbers $N=32$ and $N=34$ above proton-magic $Z=20$. In particular, they finally enable a complete and precise characterization of the trends in ground state binding energies along the $N=32$ isotone, confirming that the empirical neutron shell gap energies peak at the doubly magic $^{52}\mathrm{Ca}$. Moreover, our data, combined with other recent measurements, do not support the existence of a closed neutron shell in $^{55}\mathrm{Sc}$ at $N=34$. The results were compared to predictions from both ab initio and phenomenological nuclear theories, which all had success describing $N=32$ neutron shell gap energies but were highly disparate in the description of the $N=34$ isotone.

Background: The quadratic isobaric multiplet mass equation (IMME) has been very successful at predicting the masses of isobaric analog states in the same multiplet, while its coefficients are known to follow specific trends as functions of mass number. The Atomic Mass Evaluation 2016 [Chin. Phys. C 41, 030003 (2017)] $^{44}\mathrm{V}$ mass value results in an anomalous negative $c$ coefficient for the IMME quadratic term; a consequence of large uncertainty and an unresolved isomeric state. The $b$ and $c$ coefficients can provide useful constraints for construction of the isospin-nonconserving Hamiltonians for the $pf$ shell. In addition, the excitation energy of the ${0}^{+},T=2$ level in $^{44}\mathrm{V}$ is currently unknown. This state can be used to constrain the mass of the more exotic $^{44}\mathrm{Cr}$.Purpose: The aim of the experimental campaign was to perform high-precision mass measurements to resolve the difference between $^{44}\mathrm{V}$ isomeric and ground states, to test the IMME using the new ground state mass value and to provide necessary ingredients for the future identification of the ${0}^{+}$, $T=2$ state in $^{44}\mathrm{V}$.Method: High-precision Penning trap mass spectrometry was performed at LEBIT, located at the National Superconducting Cyclotron Laboratory, to measure the cyclotron frequency ratios of [${^{44g,m}\mathrm{VO}]}^{+}$ versus [${^{32}\mathrm{SCO}]}^{+}$, a well-known reference mass, to extract both the isomeric and ground state masses of $^{44}\mathrm{V}$.Results: The mass excess of the ground and isomeric states in $^{44}\mathrm{V}$ were measured to be $\ensuremath{-}23\phantom{\rule{4pt}{0ex}}804.9(80)$ keV/${c}^{2}$ and $\ensuremath{-}23\phantom{\rule{4pt}{0ex}}537.0(55)$ keV/${c}^{2}$, respectively. This yielded a new proton separation energy of ${S}_{p}=1\phantom{\rule{4pt}{0ex}}773(10)$ keV.Conclusion: The new values of the ground state and isomeric state masses of $^{44}\mathrm{V}$ have been used to deduce the IMME $b$ and $c$ coefficients of the lowest ${2}^{+}$ and ${6}^{+}$ triplets in $A=44$. The ${2}^{+}\phantom{\rule{4pt}{0ex}}c$ coefficient is now verified with the IMME trend for lowest multiplets and is in good agreement with the shell-model predictions using charge-dependent Hamiltonians. The mirror energy differences were determined between $^{44}\mathrm{V}$ and $^{44}\mathrm{Sc}$, in line with isospin-symmetry for this multiplet. The new value of the proton separation energy determined, to an uncertainty of 10 keV, will be important for the determination of the ${0}^{+}$, $T=2$ state in $^{44}\mathrm{V}$ and, consequently, for prediction of the mass excess of $^{44}\mathrm{Cr}$.

Background: Isobaric quintets provide the best test of the isobaric multiplet mass equation (IMME) and can uniquely identify higher order corrections suggestive of isospin symmetry breaking effects in the nuclear Hamiltonian. The generalized IMME (GIMME) is a novel microscopic interaction theory that predicts an extension to the quadratic form of the IMME. Only the $A=20,32$ $T=2$ quintets have the exotic ${T}_{z}=\ensuremath{-}2$ member ground state mass determined to high precision by Penning trap mass spectrometry.Purpose: We aim to establish $A=36$ as the third $T=2$ isobaric quintet with the ${T}_{z}=\ensuremath{-}2$ member ground state mass measured by Penning trap mass spectrometry and provide the first test of the predictive power of the GIMME.Method: A radioactive beam of neutron-deficient $^{36}\mathrm{Ca}$ was produced by projectile fragmentation at the National Superconducting Cyclotron Laboratory. The beam was thermalized and the masses of $^{36}\mathrm{Ca}^{+}$ and $^{36}\mathrm{Ca}^{2+}$ were measured by the time-of-flight ion cyclotron resonance method in the LEBIT 9.4 T Penning trap.Results: We measure the mass excess of $^{36}\mathrm{Ca}$ to be $\mathrm{ME}=\ensuremath{-}6483.6(56)$ keV, an improvement in precision by a factor of 6 over the literature value. The new datum is considered together with evaluated nuclear data on the $A=36$, $T=2$ quintet. We find agreement with the quadratic form of the IMME given by isospin symmetry, but only coarse qualitative agreement with predictions of the GIMME.Conclusion: A total of three isobaric quintets have their most exotic members measured by Penning trap mass spectrometry. The GIMME predictions in the $T=2$ quintet appear to break down for $A=32$ and greater.

We have developed and tested an experimental technique for the measurement of low-energy (p,n) reactions in inverse kinematics relevant to nuclear astrophysics. The proposed setup is located at the ReA3 facility at the National Superconducting Cyclotron Laboratory. In the current approach, we operate the beam-transport line in ReA3 as a recoil separator while tagging the outgoing neutrons from the (p,n) reactions with the low-energy neutron detector array (LENDA). The developed technique was verified by using the $^{40}$Ar(p,n)$^{40}$K reaction as a probe. The results of the proof-of-principle experiment with the $^{40}$Ar beam show that cross-section measurements within an uncertainty of $\sim$25\% are feasible with count rates up to 7 counts/mb/pnA/s. In this article, we give a detailed description of the experimental setup, and present the analysis method and results from the test experiment. Future plans on using the technique in experiments with the separator for capture reactions (SECAR) that is currently being commissioned are also discussed., Comment: Submitted to NIMA. Revised manuscript after referees' first review

Background: Ultralow $Q$-value $\ensuremath{\beta}$ decays are interesting processes to study with potential applications to nuclear $\ensuremath{\beta}$-decay theory and neutrino physics. While a number of potential ultralow $Q$-value $\ensuremath{\beta}$-decay candidates exist, improved mass measurements are necessary to determine which of these are energetically allowed.Purpose: To perform precise atomic mass measurements of $^{89}\mathrm{Y}$ and $^{139}\mathrm{La}$. Use these new measurements along with the precisely known atomic masses of $^{89}\mathrm{Sr}$ and $^{139}\mathrm{Ba}$ and nuclear energy level data for $^{89}\mathrm{Y}$ and $^{139}\mathrm{La}$ to determine if there could be an ultralow $Q$-value decay branch in the $\ensuremath{\beta}$ decay of $^{89}\mathrm{Sr}\phantom{\rule{4pt}{0ex}}\ensuremath{\rightarrow}\phantom{\rule{4pt}{0ex}}^{89}\mathrm{Y}$ or $^{139}\mathrm{Ba}\phantom{\rule{4pt}{0ex}}\ensuremath{\rightarrow}\phantom{\rule{4pt}{0ex}}^{139}\mathrm{La}$.Method: High-precision Penning trap mass spectrometry was used to determine the atomic mass of $^{89}\mathrm{Y}$ and $^{139}\mathrm{La}$, from which $\ensuremath{\beta}$-decay $Q$ values for $^{89}\mathrm{Sr}$ and $^{139}\mathrm{Ba}$ were obtained.Results: The $^{89}\mathrm{Sr}\phantom{\rule{4pt}{0ex}}\ensuremath{\rightarrow}\phantom{\rule{4pt}{0ex}}^{89}\mathrm{Y}$ and $^{139}\mathrm{Ba}\phantom{\rule{4pt}{0ex}}\ensuremath{\rightarrow}\phantom{\rule{4pt}{0ex}}^{139}\mathrm{La}\phantom{\rule{4pt}{0ex}}\ensuremath{\beta}$-decay $Q$ values were measured to be ${Q}_{\mathrm{Sr}}=1502.20(0.35)$ keV and ${Q}_{\mathrm{Ba}}=2308.37(0.68)$ keV. These results were compared to energies of excited states in $^{89}\mathrm{Y}$ at 1507.4(0.1) keV, and in $^{139}\mathrm{La}$ at 2310(19) keV and 2313(1) keV to determine $Q$ values of $\ensuremath{-}5.20(0.37)$ keV for the potential ultralow $\ensuremath{\beta}$-decay branch of $^{89}\mathrm{Sr}$ and $\ensuremath{-}1.6(19.0)$ keV and $\ensuremath{-}4.6(1.2)$ keV for those of $^{139}\mathrm{Ba}$.Conclusion: The potential ultralow $Q$-value decay branch of $^{89}\mathrm{Sr}$ to the $^{89}\mathrm{Y}$ ($3/{2}^{\ensuremath{-}}$, 1507.4 keV) state is energetically forbidden and has been ruled out. The potential ultralow $Q$-value decay branch of $^{139}\mathrm{Ba}$ to the 2313 keV state in $^{139}\mathrm{La}$ with unknown ${J}^{\ensuremath{\pi}}$ has also been ruled out at the $4\ensuremath{\sigma}$ level, while more precise energy level data is needed for the $^{139}\mathrm{La}$ ($1/{2}^{+}$, 2310 keV) state to determine if an ultralow $Q$-value $\ensuremath{\beta}$-decay branch to this state is energetically allowed.

Background: The understanding and description of forbidden decays provides interesting challenges for nuclear theory. These calculations could help to test underlying nuclear models and interpret experimental data.Purpose: Compare a direct measurement of the $^{138}\mathrm{La}\phantom{\rule{4pt}{0ex}}\ensuremath{\beta}$-decay $Q$ value with the $\ensuremath{\beta}$-decay spectrum end-point energy measured by Quarati et al. using ${\mathrm{LaBr}}_{3}$ detectors [Appl. Radiat. Isot. 108, 30 (2016)]. Use new precise measurements of the $^{138}\mathrm{La}\phantom{\rule{4pt}{0ex}}\ensuremath{\beta}$-decay and electron capture (EC) $Q$ values to improve theoretical calculations of the $\ensuremath{\beta}$-decay spectrum and EC probabilities.Method: High-precision Penning trap mass spectrometry was used to measure cyclotron frequency ratios of $^{138}\mathrm{La}$, $^{138}\mathrm{Ce}$, and $^{138}\mathrm{Ba}$ ions from which $\ensuremath{\beta}$-decay and EC $Q$ values for $^{138}\mathrm{La}$ were obtained.Results: The $^{138}\mathrm{La}\phantom{\rule{4pt}{0ex}}\ensuremath{\beta}$-decay and EC $Q$ values were measured to be ${Q}_{\ensuremath{\beta}}=1052.42(41)$ keV and ${Q}_{\mathrm{EC}}=1748.41(34)$ keV, improving the precision compared to the values obtained in the most recent atomic mass evaluation [Wang et al., Chin. Phys. C 41, 030003 (2017)] by an order of magnitude. These results are used for improved calculations of the $^{138}\mathrm{La}\phantom{\rule{4pt}{0ex}}\ensuremath{\beta}$-decay shape factor and EC probabilities. New determinations for the $^{138}\mathrm{Ce}$ 2EC $Q$ value and the atomic masses of $^{138}\mathrm{La}$, $^{138}\mathrm{Ce}$, and $^{138}\mathrm{Ba}$ are also reported.Conclusion: The $^{138}\mathrm{La}\phantom{\rule{4pt}{0ex}}\ensuremath{\beta}$-decay $Q$ value measured by Quarati et al. is in excellent agreement with our new result, which is an order of magnitude more precise. Uncertainties in the shape factor calculations for $^{138}\mathrm{La}\phantom{\rule{4pt}{0ex}}\ensuremath{\beta}$ decay using our new $Q$ value are reduced by an order of magnitude. Uncertainties in the EC probability ratios are also reduced and show improved agreement with experimental data.

Among the wide energy range of β decays, there can exist decays with Q values as low as a few hundred eV. These decays can occur when the parent decays to a excited state in the daughter nucleus. Such decays have been called “ultra-low” Q value β decays. Their application is mainly twofold: (1) they are of interest as potential candidates for neutrino mass determination experiments, and (2) they provide a testing ground for theoretical studies of atomic interference effects in the nuclear decay process. In this work we have identified a number of such potential candidates by analyzing the most recent atomic mass and nuclear energy level data. To determine if an ultra-low Q value β decay branch is energetically allowed for these candidates, more precise and accurate data for the Q value of the ultra-low decay branch is needed. In most cases, this requires more precise atomic mass measurements for the parent and/or daughter atoms. These requirements can be met using Penning trap mass spectrometry.

Nuclear structure and astrophysics studies rely heavily on precision mass measurements of rare isotopes. However, many of these isotopes far from the valley of stability can only be produced at very low rates, which are incompatible with the destructive measurement techniques used by rare isotope Penning trap mass spectrometry facilities. To this end, the Low Energy Beam and Ion Trap facility at the National Superconducting Laboratory is in the process of commissioning a single ion Penning trap (SIPT) mass spectrometer that relies on the non-destructive narrowband Fourier Transform ion cyclotron resonance technique. SIPT is the first Penning trap designed to perform mass measurements of rare isotopes produced via projectile fragmentation at rates on the order of one ion per day. The system details and cryogenic detection design, as well as results from the room and cryogenic temperature commissioning, are discussed at length.

Background: The $^{51}\mathrm{Fe}(p,\ensuremath{\gamma})^{52}\mathrm{Co}$ reaction lies along the main rp-process path leading up to the $^{56}\mathrm{Ni}$ waiting point. The uncertainty in the reaction $Q$ value, which determines the equilibrium between the forward proton-capture and reverse photodisintegration $^{52}\mathrm{Co}(\ensuremath{\gamma},p)^{51}\mathrm{Fe}$ reaction, contributes to considerable uncertainty in the reaction rate in the temperature range of interest for Type I x-ray bursts and thus to an $\ensuremath{\approx}10%$ uncertainty in burst ashes lighter than $A=56$.Purpose: With a recent Penning trap mass measurement of $^{52}\mathrm{Co}$ reducing the uncertainty on its mass to 6.6 keV [Nesterenko et al., J. Phys. G 44, 065103 (2017)], the dominant source of uncertainty in the reaction $Q$ value is now the mass of $^{51}\mathrm{Fe}$, reported in the 2016 atomic mass evaluation to a precision of 9 keV [Wang et al., Chin. Phys. C 41, 030003 (2017)]. A new, high-precision Penning trap mass measurement of $^{51}\mathrm{Fe}$ was performed to allow the determination of an improved precision $Q$ value and thus new reaction rates.Method: $^{51}\mathrm{Fe}$ was produced using projectile fragmentation at the Coupled Cyclotron Facility at the National Superconducting Cyclotron Laboratory, and separated using the A1900 fragment separator. The resulting secondary beam was then thermalized in the beam stopping area before a mass measurement was performed using the LEBIT 9.4T Penning trap mass spectrometer.Results: The new mass excess, $\mathrm{ME}=\ensuremath{-}40189.2(1.6)$ keV, is sixfold more precise than the current AME value, and $1.6\ensuremath{\sigma}$ less negative. This value was used to calculate a new proton separation energy for $^{52}\mathrm{Co}$ of 1431(7) keV. New excitation levels were then calculated for $^{52}\mathrm{Co}$ using the nushellx code with the GXPF1A interaction, and a new reaction rate and burst ash composition was calculated.Conclusions: With a new measured $Q$ value, the uncertainty on the $^{51}\mathrm{Fe}(p,\ensuremath{\gamma})$ reaction rate is dominated by the poorly measured $^{52}\mathrm{Co}$ level structure. Reducing this uncertainty would allow a more precise rate calculation and a better determination of the mass abundances in the burst ashes.

A laser ablation ion source has been developed and implemented at the Low-Energy Beam and Ion Trap (LEBIT) facility at the National Superconducting Cyclotron Laboratory. This offline ion source enhances the capabilities of LEBIT by providing increased access to ions used for calibration measurements and checks of systematic effects as well as stable and long-lived ions of scientific interest. The design of the laser ablation ion source and a demonstration of its successful operation are presented.

International audience; We discuss the motivation and technique of Penning trap mass spectrometry applied to radioactive$^{44}$V and$^{44}^{m}$V, using the LEBIT 9.4 T Penning trap mass spectrometer at the National Superconducting Cyclotron Laboratory (NSCL) at Michigan State University. A complementary measurement of these nuclides, performed at the CSRe in Lanzhou, China, was recently published, but with errors several times larger than obtainable for a short-lived radionuclide in a Penning trap. Interpretation of the higher precision results is ongoing and a full accounting of this measurement is anticipated in the coming months.

We report the mass measurement of $^{56}\mathrm{Cu}$, using the LEBIT 9.4 T Penning trap mass spectrometer at the National Superconducting Cyclotron Laboratory at Michigan State University. The mass of $^{56}\mathrm{Cu}$ is critical for constraining the reaction rates of the $^{55}\mathrm{Ni}(p,\ensuremath{\gamma})$ $^{56}\mathrm{Cu}(p,\ensuremath{\gamma})$ $^{57}\mathrm{Zn}({\ensuremath{\beta}}^{+})$ $^{57}\mathrm{Cu}$ bypass around the $^{56}\mathrm{Ni}$ waiting point. Previous recommended mass excess values have disagreed by several hundred keV. Our new value, $\mathrm{ME}=\ensuremath{-}38626.7(7.1)\text{ }\text{ }\mathrm{keV}$, is a factor of 30 more precise than the extrapolated value suggested in the 2012 atomic mass evaluation [Chin. Phys. C 36, 1603 (2012)], and more than a factor of 12 more precise than values calculated using local mass extrapolations, while agreeing with the newest 2016 atomic mass evaluation value [Chin. Phys. C 41, 030003 (2017)]. The new experimental average, using our new mass and the value from AME2016, is used to calculate the astrophysical $^{55}\mathrm{Ni}(p,\ensuremath{\gamma})$ and $^{56}\mathrm{Cu}(p,\ensuremath{\gamma})$ forward and reverse rates and perform reaction network calculations of the $rp$ process. These show that the $rp$-process flow redirects around the $^{56}\mathrm{Ni}$ waiting point through the $^{55}\mathrm{Ni}(p,\ensuremath{\gamma})$ route, allowing it to proceed to higher masses more quickly and resulting in a reduction in ashes around this waiting point and an enhancement to higher-mass ashes.

The region near Z=28, N=40 is a subject of great interest for nuclear structure studies due to spectroscopic signatures in $^{68}$Ni suggesting a subshell closure at N=40. Trends in nuclear masses and their derivatives provide a complementary approach to shell structure investigations via separation energies. Penning trap mass spectrometry has provided precise measurements for a number of nuclei in this region, however a complete picture of the mass surfaces has so far been limited by the large uncertainty remaining for nuclei with N > 40 along the iron and cobalt chains. Here we present the first Penning trap measurements of $^{68,69}$Co, performed at the Low-Energy Beam and Ion Trap facility at the National Superconducting Cyclotron Laboratory. In addition, we perform ab initio calculations of ground state and two-neutron separation energies of cobalt isotopes with the valence-space in-medium similarity renormalization group approach based on a particular set of two- and three-nucleon forces which predict saturation in infinite matter. We discuss the importance of these measurements and calculations for understanding the evolution of nuclear structure near $^{68}$Ni., 7 pages, 6 figures

A high-precision magnetometer based on a miniature Penning trap was developed to support Penning trap mass spectrometry of rare isotopes. Magnetic field monitoring with a relative precision of 2 parts in 10 8 with a temporal resolution of 15 min was demonstrated. The use of this magnetometer at the Low-Energy Beam and Ion Trap (LEBIT) facility at Michigan State University will virtually eliminate the need to perform reference measurements during on-line mass measurements of rare isotopes and allow for the best use of precious on-line measurement time.

A series of cold cathode field emission points to be used for electron impact ionization of background gas in Penning trap mass spectrometry applications have been fabricated by electrochemically etching tungsten rod in a NaOH solution. A new variation of the drop-off etching method that can produce tips with tip radii down to 10 nm is described. We present the results of studies in which the parameters used in the etching process were varied, and the geometry and operation of the resulting tips was investigated by imaging them with a scanning electron microscope and by operating them in field emission mode. Finally, the use of these tips in a Penning trap mass spectrometry application is described.

Using high-precision Penning trap mass spectrometry at the Low Energy Beam and Ion Trap facility at the National Superconducting Cyclotron Laboratory we have measured the $Q$ values of the fourth-order forbidden $\ensuremath{\beta}$ decay and electron capture of $^{50}\mathrm{V}$ and the double electron capture $Q$ value of $^{50}\mathrm{Cr}$ with the results ${Q}_{\ensuremath{\beta}}(^{50}\mathrm{V})=1038.1(1)$ keV, ${Q}_{\mathrm{EC}}(^{50}\mathrm{V})=2208.7(1)$ keV, and ${Q}_{2\mathrm{EC}}(^{50}\mathrm{Cr})=1170.5(1)$ keV. In addition, we have measured the atomic masses of $^{46,47,49,50}\mathrm{Ti},^{50,51}\mathrm{V}$, and $^{50,52--54}\mathrm{Cr}$, reducing uncertainties by factors of up to three compared with the most recent atomic mass evaluation $(Ame2016)$ [Chin. Phys. C 41, 030003 (2017)]. Our results are in good agreement with $Ame2016$ for $^{46,47,49,50}\mathrm{Ti}$ and $^{50,54}\mathrm{Cr}$ and show deviations of up to $\ensuremath{\sim}1\phantom{\rule{4pt}{0ex}}\mathrm{keV}\phantom{\rule{4pt}{0ex}}(2.5\ensuremath{\sigma})$ for $^{50,51}\mathrm{V}$ and $^{50,54}\mathrm{Cr}$.

During the next several years and decades the extension of high-precision Penning trap mass spectrometry measurements to more-exotic isotopes, lying far from the valley of stability will continue to provide significant contributions to nuclear physics. However, such measurements must overcome the challenges of working with isotopes that have low production rates and short lifetimes. At the Low Energy Beam and Ion Trap (LEBIT) facility at the National Superconducting Cyclotron Laboratory, a number of developments have been implemented or are underway to meet these challenges by minimizing rare-isotope preparation and measurement time, maximizing use of available beam time, and increasing sensitivity. These developments and the current status of the LEBIT facility will be discussed.

Background: The observation of neutrinoless double-$\ensuremath{\beta}$ transitions would indicate physics beyond the standard model as the lepton number conservation is violated. For a complete degeneracy in the energy of the initial and final states, the neutrinoless double-electron capture is resonantly enhanced. This shortens the half-life to similar orders of magnitude as the neutrinoless double-$\ensuremath{\beta}$ decay and expands the set of nuclei for the search of neutrinoless double-$\ensuremath{\beta}$ transitions as the observation of either process would be equally likely.Purpose: To clearly identify transitions that are resonantly enhanced, among other parameters the total energy of the decay, ${Q}_{\ensuremath{\varepsilon}\ensuremath{\varepsilon}}$, needs to be measured very precisely. Of the 12 initially identified candidates, the last remaining decay without a precise ${Q}_{\ensuremath{\varepsilon}\ensuremath{\varepsilon}}$ was $^{190}\mathrm{Pt}(0\ensuremath{\nu}\ensuremath{\varepsilon}\ensuremath{\varepsilon})^{190}\mathrm{Os}$.Method: The ${Q}_{\ensuremath{\varepsilon}\ensuremath{\varepsilon}}$ value was determined with the Penning trap mass spectrometer LEBIT by measuring the ratio of the cyclotron frequencies of $^{190}\mathrm{Pt}^{+}$ and $^{190}\mathrm{Os}^{+}$ in a 9.4-T superconducting magnet.Result: The ${Q}_{\ensuremath{\varepsilon}\ensuremath{\varepsilon}}$ value was determined to be 1401.57(47) keV with an uncertainty reduction of an order of magnitude compared to its previously known value. The absolute value is shifted by 17.17(623) keV relative to the previously accepted one. Furthermore, the mass value of $^{190}\mathrm{Pt}$ was found to be shifted by more than three standard deviations. In addition we improved the mass values for $^{186,190}\mathrm{Os}$ and $^{194}\mathrm{Pt}$.Conclusion: Transitions to the two nuclear excited states of $^{190}\mathrm{Os}$ with 1326.9(5) and 1387.00(2) keV energy were identified to be resonantly enhanced within a $1\ensuremath{\sigma}$ uncertainty. The significantly reduced uncertainty of ${Q}_{\ensuremath{\varepsilon}\ensuremath{\varepsilon}}$ confirmed the potential for a resonantly enhanced transition.

A new variation of the drop-off method for fabricating field emission points by electrochemically etching tungsten rods in a NaOH solution is described. The results of studies in which the etching current and the molarity of the NaOH solution used in the etching process were varied are presented. The investigation of the geometry of the tips, by imaging them with a scanning electron microscope, and by operating them in field emission mode is also described. The field emission tips produced are intended to be used as an electron beam source for ion production via electron impact ionization of background gas or vapor in Penning trap mass spectrometry applications.

We report the determination of the Q(EC) value of the mirror transition of (11)C by measuring the atomic masses of (11)C and (11)B using Penning trap mass spectrometry. More than an order of magnitude improvement in precision is achieved as compared to the 2012 Atomic Mass Evaluation (Ame2012) [Chin. Phys. C 36, 1603 (2012)]. This leads to a factor of 3 improvement in the calculated Ft value. Using the new value, Q(EC)=1981.690(61) keV, the uncertainty on Ft is no longer dominated by the uncertainty on the Q(EC) value. Based on this measurement, we provide an updated estimate of the Gamow-Teller to Fermi mixing ratio and standard model values of the correlation coefficients.

The LEBIT (Low Energy Beam and Ion Trap) facility is the only Penning trap mass spectrometry (PTMS) facility to utilize rare isotopes produced via fast-beam fragmentation. This technique allows access to practically all elements lighter than uranium, and in particular enables the production of isotopes that are not available or that are difficult to obtain at isotope separation on-line facilities. The preparation of the high-energy rare-isotope beam produced by projectile fragmentation for low-energy PTMS experiments is achieved by gas stopping to slow down and thermalize the fast-beam ions, along with an rf quadrupole cooler and buncher and rf quadrupole ion guides to deliver the beam to the Penning trap. During its first phase of operation LEBIT has been very successful, and new developments are now underway to access rare isotopes even farther from stability, which requires dealing with extremely short lifetimes and low production rates. These developments aim at increasing delivery efficiency, minimizing delivery and measurement time, and maximizing use of available beam time. They include an upgrade to the gas-stopping station, active magnetic field monitoring and stabilization by employing a miniature Penning trap as a magnetometer, the use of stored waveform inverse Fourier transform (SWIFT) to most effectively remove unwanted ions, and charge breeding.

We present a summary of precision atomic mass measurements of stable isotopes carried out at Florida State University. These include the alkalis 6Li, 23Na, 39,41K, 85,87Rb, 133Cs; the rare gas isotopes 84,86Kr and 129,130,132,136Xe; 17,18O, 19F, 28Si, 31P, 32S; and various isotope pairs of importance to neutrino physics, namely 74,76Se/74,76Ge, 130Xe/130Te, and 115In/115Sn. We also summarize our Penning trap measurements of the dipole moments of PH + and HCO + .

A brief review is presented of recent work with the Precision Penning Trap Mass Spectrometer, formerly at MIT, now at Florida State University. This includes atomic mass comparisons using single trapped ions; mass comparisons using two simultaneously trapped ions alternated between large and small cyclotron radii; and measurement of the dipole moment of a molecular ion using the polarizability-induced shift in cyclotron frequency.

We report the first direct measurement of the $^{14}\mathrm{O}$ superallowed Fermi $\ensuremath{\beta}$-decay ${Q}_{EC}$ value, the last of the so-called ``traditional nine'' superallowed Fermi $\ensuremath{\beta}$ decays to be measured with Penning trap mass spectrometry. $^{14}\mathrm{O}$, along with the other low-$Z$ superallowed $\ensuremath{\beta}$ emitter, $^{10}\mathrm{C}$, is crucial for setting limits on the existence of possible scalar currents. The new ground state ${Q}_{EC}$ value, 5144.364(25) keV, when combined with the energy of the ${0}^{+}$ daughter state, ${E}_{x}({0}^{+})=2312.798(11)\text{ }\text{ }\mathrm{keV}$ [, Nucl. Phys. A523, 1 (1991)], provides a new determination of the superallowed $\ensuremath{\beta}$-decay ${Q}_{EC}$ value, ${Q}_{EC}(\mathrm{sa})=2831.566(28)\text{ }\text{ }\mathrm{keV}$, with an order of magnitude improvement in precision, and a similar improvement to the calculated statistical rate function $f$. This is used to calculate an improved $\mathcal{F}t$ value of 3073.8(2.8) s.

Experimental searches for neutrinoless double-$\ensuremath{\beta}$ decay offer one of the best opportunities to look for physics beyond the standard model. Detecting this decay would confirm the Majorana nature of the neutrino, and a measurement of its half-life can be used to determine the absolute neutrino mass scale. Important to both tasks is an accurate knowledge of the $Q$ value of the double-$\ensuremath{\beta}$ decay. The LEBIT Penning trap mass spectrometer was used for the first direct experimental determination of the $^{96}\mathrm{Zr}$ double-$\ensuremath{\beta}$ decay $Q$ value: ${Q}_{\ensuremath{\beta}\ensuremath{\beta}}=3355.85(15)$ keV. This value is nearly 7 keV larger than the 2012 Atomic Mass Evaluation [M. Wang et al., Chin. Phys. C 36, 1603 (2012)] value and one order of magnitude more precise. The 3-$\ensuremath{\sigma}$ shift is primarily due to a more accurate measurement of the $^{96}\mathrm{Zr}$ atomic mass: $m{(}^{96}\mathrm{Zr})=95.908\phantom{\rule{0.16em}{0ex}}277\phantom{\rule{0.16em}{0ex}}35(17)$ u. Using the new $Q$ value, the $2\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$-decay matrix element, $|{M}_{2\ensuremath{\nu}}|$, is calculated. Improved determinations of the atomic masses of all other zirconium $(^{90\ensuremath{-}92,94,96}\mathrm{Zr})$ and molybdenum $({}^{92,94\ensuremath{-}98,100}\mathrm{Mo})$ isotopes using both ${}^{12}{\mathrm{C}}_{8}$ and $^{87}\mathrm{Rb}$ as references are also reported.

At Central Michigan University we are developing a high-precision Penning trap mass spectrometer (CHIP-TRAP)that will focus on measurements with long-lived radioactive isotopes. CHIP-TRAP will consist of a pair of hyperbolic precision-measurement Penning traps, and a cylindrical capture/filter trap in a 12 T magnetic field. Ions will be produced by external ion sources, including a laser ablation source, and transported to the capture trap at low energies enabling ions of a given m=q ratio to be selected via their time-of-flight. In the capture trap, contaminant ions will be removed with a mass-selective rf dipole excitation and the ion of interest will be transported to the measurement traps. A phase-sensitive image charge detection technique will be used for simultaneous cyclotron frequency measurements on single ions in the two precision traps, resulting in a reduction in statistical uncertainty due to magnetic field fluctuations., Comment: 5 pages, submitted to NIMB (EMIS 2015 Conference Proceedings)

We have implemented a technique for precision mass comparison of two ions trapped simultaneously in a Penning trap in which each ion is alternately positioned at the center of the trap – where the cyclotron frequency is measured – and in a large cyclotron “parking” orbit. Systematic shifts in the cyclotron frequency ratio have been studied by comparing 13 C 2 H 2 + / 14 N 2 + and 14 N 2 + / 28 Si + . Using the method to compare 28 SiH 3 + / 31 P + we have obtained a new atomic mass for 31 P, M[ 31 P] = 30.973 761 999 7 (61) u.

Penning-trap mass spectrometry was used at the Low-Energy Beam and Ion Trap (LEBIT) facility at the National Superconducting Cyclotron Laboratory (NSCL) to investigate ${}^{78}$Kr, a candidate for resonantly enhanced neutrinoless double-electron capture (0$\ensuremath{\nu}$ECEC). The newly determined $Q$ value of 2847.75 (27) keV is 1.4 keV greater than the value from the most recent atomic mass evaluation [Chin. Phys. C 36, 1603 (2012)], a change of two sigma, and the uncertainty has been reduced by a factor of three. The change in the $Q$ value shifts allowed 0$\ensuremath{\nu}$ECEC in ${}^{78}$Kr further from resonant enhancement. With the improved determination of the $Q$ value, all known excited states can now be confidently excluded from possible ${}^{78}$Se candidates that could lead to resonantly enhanced 0$\ensuremath{\nu}$ECEC.

The low-energy beam and ion trap Penning trap mass spectrometer was used for an improved determination of the ${}^{48}\mathrm{Ca}$ double-$\ensuremath{\beta}$ decay $Q$ value: ${Q}_{\ensuremath{\beta}\ensuremath{\beta}}=4268.121(79)\phantom{\rule{0.28em}{0ex}}\mathrm{keV}$. The new value is 1.2 keV greater than the value in the 2012 atomic mass evaluation [Chin. Phys. C 36, 1603 (2012)], a shift of three $\ensuremath{\sigma}$, and is a factor of 5 more precise. Accurate knowledge of this $Q$ value is important for experimental searches to observe neutrinoless double-$\ensuremath{\beta}$ decay (0$\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$) in ${}^{48}\mathrm{Ca}$ and is essential for extracting the effective mass of the electron neutrino if the ${}^{48}\mathrm{Ca}$ half-life of 0$\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$ was experimentally determined.

In anticipation of results from current and future double-$\ensuremath{\beta}$ decay studies, we report a measurement resulting in a $^{82}\mathrm{Se}$ double-$\ensuremath{\beta}$ decay $Q$ value of 2997.9(3) keV, an order of magnitude more precise than the currently accepted value. We also present preliminary results of a calculation of the $^{82}\mathrm{Se}$ neutrinoless double-$\ensuremath{\beta}$ decay nuclear matrix element that corrects in part for the small size of the shell model single-particle space. The results of this work are important for designing next generation double-$\ensuremath{\beta}$ decay experiments and for the theoretical interpretations of their observations.

The possibility of detecting neutrinoless double-$\ensuremath{\beta}$-decay (0$\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$-decay) in experiments that are currently in operation or under development provides the exciting opportunity to determine the Dirac or Majorana nature of the neutrino and its absolute mass scale. An important datum for interpreting 0$\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$-decay experimental results is the $Q$ value of the decay. Using Penning trap mass spectrometry we have measured the atomic mass of ${}^{48}$Ca to be $M{[}^{48}$Ca] $=$ 47.952 522 76(21) u which, combined with the mass of ${}^{48}$Ti evaluated by Audi et al. [Nucl. Phys. A 729, 337 (2003)], provides a new determination of the ${}^{48}$Ca $\ensuremath{\beta}\ensuremath{\beta}$-decay $Q$ value: ${Q}_{\ensuremath{\beta}\ensuremath{\beta}}$ $=$ 4262.96(84) keV.

In anticipation of results from current and future double-β decay studies, we report a measurement resulting in a (82)Se double-β decay Q value of 2997.9(3) keV, an order of magnitude more precise than the currently accepted value. We also present preliminary results of a calculation of the (82)Se neutrinoless double-β decay nuclear matrix element that corrects in part for the small size of the shell model single-particle space. The results of this work are important for designing next generation double-β decay experiments and for the theoretical interpretations of their observations.

Using single ions in a precision cryogenic Penning trap and by measuring the small shifts in their cyclotron frequencies due to their electric polarizability, the ground-state electric dipole moments of HCO${}^{+}$ and NH${}^{+}$ have been determined. The results are \ensuremath{\mu}(HCO${}^{+}$) $=$ 1.543(12) $e{a}_{0}$ and \ensuremath{\mu}(NH${}^{+}$) $=$ 0.782(11) $e{a}_{0}$, which agree with theoretical predictions.

The atomic masses of the alkali-metal isotopes $^{6}\mathrm{Li},^{23}\mathrm{Na},^{39,41}\mathrm{K},^{85,87}\mathrm{Rb}$, and $^{133}\mathrm{Cs}$ have been obtained from measurements of cyclotron frequency ratios of pairs of ions simultaneously trapped in a Penning trap. The results, with one standard deviation uncertainty, are: $M(^{6}\mathrm{Li})=6.015 122 887 4(16)\mathrm{u},M(^{23}\mathrm{Na})=22.989769 282 8(26)\mathrm{u},M(^{39}\mathrm{K})=38.963 706 485 6(52)\mathrm{u},M(^{41}\mathrm{K})=40.961 825 257 4(48)\mathrm{u},M(^{85}\mathrm{Rb})=84.911 789739(9)\mathrm{u},M(^{87}\mathrm{Rb})=86.909 180 535(10)\mathrm{u}$, and $M(^{133}\mathrm{Cs})=132.905 451 963(13)\mathrm{u}$. Our mass of $^{6}\mathrm{Li}$ yields an improved neutron separation energy for $^{7}\mathrm{Li}$ of 7251.1014(45) keV.

By fitting the Dunham-Watson model to extensive rotational and vibrational spectroscopic data of isotopic variants of CO, and by using existing precise masses of {sup 13}C,{sup 16}O, and {sup 18}O from Penning-trap mass spectrometry, we determine the atomic mass of {sup 17}O to be M[{sup 17}O]=16.999 131 644(30) u, where the uncertainty is purely statistical. Using Penning-trap mass spectrometry, we have also directly determined the atomic mass of {sup 17}O with the more precise result M[{sup 17}O]=16.999 131 756 6(9) u. The Dunham-Watson model applied to the molecular spectroscopic data hence predicts the mass of {sup 17}O to better than 1 part in 10{sup 8}.

Using precision, cryogenic, Penning-trap mass spectrometry we have measured the atomic mass difference $M[^{115}\mathrm{In}]--M[^{115}\mathrm{Sn}]$ to be $497.489(10)\text{ }\text{ }\mathrm{keV}/{c}^{2}$. Combined with the energy of the $3/{2}^{+}$ first excited state of $^{115}\mathrm{Sn}$ [J. Blachot, Nuclear Data Sheets 104, 967 (2005)], the $Q$ value of the $^{115}\mathrm{In}(9/{2}^{+})\ensuremath{\rightarrow}^{115}\mathrm{Sn}(3/{2}^{+})$ beta decay is determined to be 155(24) eV. This confirms the inference of Cattadori et al. [Nucl. Phys. A 748, 333 (2005)] that this small branching-ratio beta decay has the lowest-known $Q$ value. We also report improved values of the individual atomic masses: $M[^{115}\mathrm{In}]=114.903\text{ }878\text{ }774(16)\text{ }\text{ }\mathrm{u}$ and $M[^{115}\mathrm{Sn}]=114.903\text{ }344\text{ }697(17)\text{ }\text{ }\mathrm{u}$.

The atomic masses of $^{130}\mathrm{Te}$ and $^{130}\mathrm{Xe}$ have been obtained by measuring cyclotron frequency ratios of pairs of triply charged ions simultaneously trapped in a Penning trap. The results, with 1 standard deviation uncertainty, are $M(^{130}\mathrm{Te})=129.906\text{ }222\text{ }744(16)\text{ }\mathrm{u}$ and $M(^{130}\mathrm{Xe})=129.903\text{ }509\text{ }351(15)\text{ }\mathrm{u}$. From the mass difference the double-$\ensuremath{\beta}$-decay $Q$ value of $^{130}\mathrm{Te}$ is determined to be ${Q}_{\ensuremath{\beta}\ensuremath{\beta}}(^{130}\mathrm{Te})=2527.518(13)\text{ }\text{ }\mathrm{keV}$. This is a factor of 150 more precise than the result of the AME2003 [G. Audi et al., Nucl. Phys. A729, 337 (2003)].

Using precision, cryogenic, Penning-trap mass spectrometry we have measured the atomic mass difference M[;{115}In]-M[;{115}Sn] to be 497.489(10) keV/c;{2}. Combined with the energy of the 3/2;{+} first excited state of ;{115}Sn [J. Blachot, Nuclear Data Sheets 104, 967 (2005)10.1016/j.nds.2005.03.003], the Q value of the ;{115}In(9/2;{+}) --;{115}Sn(3/2;{+}) beta decay is determined to be 155(24) eV. This confirms the inference of Cattadori [Nucl. Phys. A 748, 333 (2005)10.1016/j.nuclphysa.2004.10.025] that this small branching-ratio beta decay has the lowest-known Q value. We also report improved values of the individual atomic masses: M[;{115}In] = 114.903 878 774(16) u and M[;{115}Sn] = 114.903 344 697(17) u.

The atomic masses of 130Te and 130Xe have been obtained by measuring cyclotron frequency ratios of pairs of triply charged ions simultaneously trapped in a Penning trap. The results, with 1 standard deviation uncertainty, are M(130Te)=129.906 222 744(16) u and M(130Xe)=129.903 509 351(15) u. From the mass difference the double-beta-decay Q value of 130Te is determined to be Qbetabeta(130Te)=2527.518(13) keV. This is a factor of 150 more precise than the result of the AME2003 [G. Audi, Nucl. Phys. A729, 337 (2003)10.1016/j.nuclphysa.2003.11.003].

By trapping pairs of ions in a Penning trap, alternating each ion between large and small cyclotron orbits, we have measured the cyclotron frequency ratios 12C2H4+/28Si+, 13C2H2+/28Si+, 28SiH3+/31P+, and 16O2+/31PH+, all to